Thin film evaporation is a process of physical vapor deposition that is used to create thin films of a material. Most commonly used for metal films and solar rooftops, thin film evaporation uses different technologies to evaporate larger pieces of the material in a vacuum chamber to leave behind a thin, even layer on a surface. The most widely used process of thin film evaporation involves heating and evaporating the target material itself, then allowing it to condense on the substrate, or surface, that receives the thin film.
This process typically begins in a sealed vacuum chamber, which is optimized to draw up vapor and gaseous particles by reducing the air pressure and crowding of other air molecules. Not only does this reduce the energy needed to evaporate, but it also allows for a more direct path to the area of deposition because the vapor particles do not get bounced around by as many other particles within the chamber. Poor chamber construction with more air pressure will reduce these vacuum effects, causing the resulting thin film to become less smooth and uniform.
The are two main strategies for vaporizing the target material are electron beam evaporation and filament evaporation. Electron beam techniques involve heating the source material to high temperatures by bombarding it with a stream of electrons, which are directed by a magnetic field. Tungsten is typically used as the source of the electrons, and it can produce more heat for the material than filament evaporation techniques. Although electron beams can achieve higher temperatures, they can also create unintentional harmful side effects, such as x-rays, which could potentially damage the materials within the chamber. Annealing processes can eliminate these effects.
Filament evaporation is the second method for inducing evaporation in the material, and it involves heating through resistive elements. Usually resistance is created by feeding current through a stable resistor, generating enough heat to melt and then vaporize the material. While this process could slightly increase the likelihood of contamination, it can create fast rates of deposition that average to about 1 nm per second.
Compared to other methods of vapor deposition, such as sputtering and chemical vapor deposition, thin film evaporation offers a few key advantages and disadvantages. Some of the drawbacks include less surface uniformity and decreased step coverage. Advantages include faster deposition rates, especially when compared with sputtering, and fewer high-speed ions and electrons, which are frequent in sputtering processes.